1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing techniques and, more particularly, to slurries utilized in chemical-mechanical polishing.
2. Prior Art
The manufacture of an integrated circuit device requires the formation of various layers (both conductive and non-conductive) above a base substrate to form the necessary components and interconnects. During the manufacturing process, removal of a certain layer or portions of a layer must be achieved in order to pattern and form various components and interconnects. Generally, this removal process is termed "etching."
One of the techniques available for removal of material from a semiconductor wafer is known as the chemical-mechanical polishing (CMP) process, in which a chemical slurry is used along with a polishing pad. The mechanical movement of the pad relative to the wafer in combination with the chemical reaction of the slurry provide the abrasive force for removing the exposed surface of the wafer. A variety of CMP tools are available to perform this type of polishing. Improvements are currently being sought in the areas of pad and slurry composition and usage, all to obtain better control over existing CMP practices.
One area of CMP pertains to the removal of metallic materials. CMP of metals can be used to define vertical and horizontal wiring in semiconductor wafers, such as a silicon wafer. This process requires high selectivity in removal rate of metals versus dielectric surfaces, such as a silicon dioxide layer, to insure small oxide erosion on patterned structures. Silicon dioxide (SiO.sub.2) abrasives are commonly used to polish dielectric layers. However, because alumina particles have lower chemical reactivity than silica particles on SiO.sub.2, CMP of a metal layer is predominantly accomplished with alumina slurries to provide acceptable selectivity. Without this higher selectivity, undesirable amounts of the SiO.sub.2 layer will be polished away with the metal. However, there are a number of disadvantages associated with the use of alumina slurries.
Alumina slurries are generally more costly to use as compared to silica slurries. The added cost increases the cost of manufacturing integrated circuits on wafers. Generally, alumina slurries are defect prone and are more difficult to disperse than silica slurries. The defects are the result of scratches left on the polished surface by the alumina slurry, mainly due to the polishing by larger size and harder alumina particles.
Thus, it is appreciated that reliance on silica slurries is more beneficial than using alumina slurries for polishing metals, but only if the selectivity is sufficiently high to limit the erosion of oxide layers to an acceptable level. Accordingly, the present invention addresses a way of obtaining this higher selectivity using silica-based slurries to polish metal.